There are JavaScript APIs in the loader you can call directly, but they will be asynchronously loaded and executed (so you'll need to pass in a callback)
Basically the only way to get this asynchronously loading / synchronously executing behavior is to statically analyze your "root" module for dependencies and load them (and their dependencies, etc). Once they're all loaded you can begin execution and synchronously execute every module as they're imported.
FYI CommonJS (not AMD) loaders for the browser do the same thing to avoid synchronous XHRs that will cause the UI to hang.
Basically the only way to get this asynchronously loading / synchronously executing behavior is to statically analyze your "root" module for dependencies and load them (and their dependencies, etc). Once they're all loaded you can begin execution and synchronously execute every module as they're imported.
FYI CommonJS (not AMD) loaders for the browser do the same thing to avoid synchronous XHRs that will cause the UI to hang.